1. Field of the Invention
This invention relates generally to an exposure control system with an inertial wheel for controlling the opening movement of the shutter blade elements in a photographic apparatus, and more particularly, to an exposure control system with "scanning type" shutter blade elements in which the opening rate of movement of the blades is slowed by way of an inertial wheel while the closing rate of movement remains substantially unaffected.
2. Description of the Prior Art
Exposure control systems for photographic camera apparatus generally embody lightweight shutter blade elements with scene light admitting apertures therethrough. The shutter blade elements may be moved in directions which operate to progressively enlarge and decrease the effective scene light admitting aperture. The rate at which the shutter blade elements are moved determines the rate at which the effective aperture increases and decreases and has a direct influence on the achievable depth of field. Thus, in order to increase the depth of field, it may be desirable to slow the speed of the shutter blade elements as they are moved in the direction of progressively increasing effective aperture size. Shutter blade elements are often moved toward the opening position through the influence of a biasing spring, the output force characteristic of which controls the speed at which the shutter blade elements move. For exposure control systems embodying lightweight shutter blade elements, as well as other moving components, it may be necessary to utilize a substantially light biasing spring to achieve the desired slow rate of blade opening. However, in such a lightweight exposure control system of the above described type, where the actuating force is small, the frictional forces between moving components becomes a significant part of the overall force which must be overcome by the biasing means. These frictional forces also tend to vary with shutter blade movement and thus may cause a jerking movement of the shutter blades which is highly undesirable. An increase in the output force characteristic of the biasing spring by itself may make the opening movement of the shutter blade elements less sensitive to frictional force variations; however, the increased shutter blade speed will also limit the depth of field which could otherwise be achieved.
One means of slowing the opening shutter blade speed without increasing the weight of the exposure control components is disclosed in a U.S. Pat. No. 3,969,738 entitled "Exposure Control System with Inertia Characteristic", by B. Johnson et al. issued July 13, 1976 in common assignment herewith, which discloses an exposure control system of the type embodying "scanning type" shutter blade elements wherein means are included for selectively presenting a relatively high inertial characteristic to the shutter blade elements as they are moved toward their maximum scene light admitting position. The inertial characteristic is presented by means of an inertial member disposed of copivotal movement with respect to the shutter blade mounting member or walking beam. Thus, the inertial characteristic imparted to the opening shutter blade elements is determined by the weight of the inertial member. Another such inertial exposure control system embodying an inertial member copivotally disposed with the walking beam is disclosed in U.S. Pat. No. 3,969,739 entitled "Exposure Control System with Selectively Presentable Inertia Member", by B. Johnson et al., issued July 13, 1976 in common assignment herewith. Wherein such inertial members operate in a satisfactory manner for the purposes in which they were intended, it may be desirable to slow the opening shutter blade movement even more, particularly for cameras of the non-focusing type where an increased depth of field is particularly desirable. It may not be possible to achieve the desired slow rate of opening blade movement solely by increasing the size and weight of the aforementioned inertial members and still maintain a compact photographic camera structure.
Therefore, it is an object of this invention to provide an exposure camera system embodying "scanning type" shutter blade elements wherein the opening movement of the shutter blades may be slowed to a greater extent than was heretofore possible to provide an increased depth of field without materially increasing the size of the exposure control system.
It is another object of this invention to provide an exposure control system having "scanning type" shutter blade elements where means are provided to increase the inertial characteristic of the shutter blade elements during their opening movement so as to slow the shutter blade elements and effect a corresponding increase in the depth of field in a simple and economical manner.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.